1. Field of the Invention
The present invention relates to multilayered common-mode choke coils, for example, common-mode choke coils for use with a sound signal.
2. Description of the Related Art
A conventional multilayered common-mode choke coil 60 shown in FIG. 8 has been known as a common-mode choke coil which prevents noise having the same phase from passing. The common-mode choke coil 60 includes a plurality of coils in which the diameters of coil portions are substantially equal to each other and the axes of the coil portions are aligned collinearly. The multilayered common-mode choke coil 60 includes insulating sheets 61 having surfaces that are provided with coil conductors 62 to 69, respectively.
The coil conductors 62 to 65 are electrically connected in series through via-holes 75a to 75c provided in some of the insulating sheets 61 so as to define a spiral coil La having an axis which is parallel to the laminating direction of the insulating sheets 61. The coil conductors 66 to 69 are electrically connected in series through via-holes 75d to 75f provided in some of the other insulating sheets 61 so as to define a spiral coil Lb having an axis which is parallel to the laminating direction of the insulating sheets 61.
The coil conductor 62 has an extended portion 62a, which is exposed at the left on the back portion of one of the sheets 61 and which functions as the input-side extended portion of the coil La. The coil conductor 65 has an extended portion 65a, which is exposed at the left on the front portion of one of the sheets 61 and which functions as the output-side extended portion of the coil La. Furthermore, a coil portion 62b of the coil conductor 62, the coil conductors 63 and 64, and a coil portion 65b of the coil conductor 65 are spirally wound by 1.75 turns so as to define a coil portion 70 of the coil La.
On the other hand, the coil conductor 69 has an extended portion 69a, which is exposed at the right on the back portion of one of the sheets 61 and which functions as the input-side extended portion of the coil Lb. The coil conductor 66 has an extended portion 66a, which is exposed at the right on the front portion of one of the sheets 61 and which functions as the output-side extended portion of the coil Lb. Furthermore, a coil portion 66b of the coil conductor 66, the coil conductors 67 and 68, and a coil portion 69b of the coil conductor 69 are spirally wound by 2.25 turns so as to define a coil portion 71 of the coil Lb.
Each of the sheets 61 is laminated and then is integrally baked so that a laminated body 80 as shown in FIG. 9 is produced. An input electrode 81a of the coil La and an input electrode 82a of the coil Lb are located on the back surface of the laminated body 80, and an output electrode 81b of the coil La and an output electrode 82b of the coil Lb are located on the front surface of the laminated body 80.
As shown in FIG. 10, the input-side extended portion 62a of the coil La is electrically connected to the input electrode 81a and the output-side extended portion 65a is electrically connected to the output electrode 81b. Also, the input-side extended portion 69a of the coil Lb is electrically connected to the input electrode 82a and the output-side extended portion 66a is electrically connected to the output electrode 82b. The extended portions 62a, 65a, 66a, and 69a connect the input/output electrodes 81a to 82b and the coil portions 70 and 71 linearly with the shortest distance.
In the known common-mode choke coil 60, a 0.5-turn difference is inevitably caused between the two spiral coils La and Lb. Therefore, the line length of the coil La is different from that of the coil Lb, and thus difference in transmission delay is generated between the coils La and Lb. Consequently, a problem arises, that is, the suppression characteristic of an in-phase signal (in-phase suppression characteristic) is poor. Accordingly, the known common-mode choke coil 60 has been used only for a signal transmission line or a power supply line for a signal in a low frequency band, in which the difference in transmission delay between the coils La and Lb can be ignored.
Recently, however, difference in the number of coil turns cannot be ignored because a transmission signal of higher frequency has been used and a differential signal transmission method has been adopted. For example, in the differential signal transmission method, transmission delay is caused in accordance with the difference in the number of coil turns (difference in the length of transmission line of coils). Also, the balance of differential signal transmission is lost.
In order to solve the problems described above, preferred embodiments of the present invention provide a multilayered common-mode choke coil in which transmission delay is prevented from occurring in a high-frequency band and a balance of a transmission signal is not lost in differential signal transmission.
According to a preferred embodiment of the present invention, a multilayered common-mode choke coil includes a laminated body having a plurality of insulating layers and a plurality of coil conductors laminated together, and at least two spiral coils which are defined by electrically connecting the coil conductors and which includes extended portions and coil portions. The diameters of the coil portions of the at least two spiral coils are substantially the same, the axes of the coil portions are aligned collinearly, and the two spiral coils are aligned in the laminating direction of the insulating layers. The extended portions of the spiral coils are extended on the insulating layers and junctions of the extended portions and the coil portions are located at substantially the center in a predetermined direction of the insulating layers so that the lengths of the coil portions of the spiral coils are substantially equal to each other.
According to another preferred embodiment of the present invention, a multilayered common-mode choke coil includes a laminated body having a plurality of insulating layers and a plurality of coil conductors laminated together, and three spiral coils which are defined by electrically connecting the coil conductors and which includes extended portions and coil portions. The diameters of the coil portions of the three spiral coils are substantially the same, the axes of the coil portions are aligned collinearly, and the three spiral coils are aligned in the laminating direction of the insulating layers. Each of the three spiral coils preferably has a trifiler configuration. A spiral coil positioned at the approximate center in the laminating direction of the insulating layers is connected to a ground electrode. In two spiral coils positioned at the top and the bottom in the laminating direction of the insulating layers, the extended portions of the spiral coils are extended on the insulating layers and junctions of the extended portions and the coil portions are located at substantially the center in a predetermined direction of the insulating layers so that the lengths of the coil portions of the two spiral coils are substantially equal to each other.
With this arrangement, the junction of each of the extended portions and each of the coil portions of the spiral coils may have a folded configuration. Also, the number of turns and the line length of the spiral coils are substantially equal so that a difference in delay of signal transmission between the coils can be prevented.
Preferably, when the laminated body is seen through, the junctions of the extended portions and the coil portions of the plurality of spiral coils do not overlap. With this arrangement, a local internal stress caused at the junctions of the extended portions and the coil portions is dispersed when the laminated body, which is constructed by laminating the insulating layers and the coil conductors, is baked. Thus, breaking and cracking of the laminated body is reliably prevented when the laminated body is baked.
Further, the plurality of spiral coils are constructed by electrically connecting the plurality of coil conductors through via-holes provided in the insulating layers, and, when the laminated body is seen through, via-holes connected to the coil conductors having input-side extended portions are located at the same position and via-holes connected to the coil conductors having output-side extended portions are located at the same position. With this arrangement, the pattern shapes of the coil conductors defining the coil portions of the spiral coils and the laminating order may be the same, except for the coil conductors which have the extended portion. Accordingly, the types of patterns of the coil conductor decrease and manufacturing efficiency of the multilayered common-mode choke coil is greatly improved so that the manufacturing cost can be remarkably reduced.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.